Coal-rock sensing system



s. l. PERssoN ETAL 2,944,804

COAL-Roux sENsING SYSTEM July l2, 1960 Filed Sept. 9, 1958 4 Sheets-Sheet 1 I Il Illlllllllllllllll/Ullllllllllllllllllll llllllllllllllllllll I E f n 5 a.- 6 'ff "fi y r 4 INVENTORS. STEN l. PERSSON WILLIAM A. LEET T ORNEY July l2, 1960 s. l. PERssoN ETAL COAL-ROCK SENSING SYSTEM Filed Sept. 9. 1958 4 Sheets-Sheet 2 SPRING v FIG. 4

GATE 44 July 12, 1960 y s. l. PERssoN ETAL 2,944,804

COAL-ROCK SENSING SYSTEM Filed Sept. 9, 1958 4 She'ets-Sheet 5 DIRECTION OF MOTION DISPLACEMENT TIME VO LTS OUTPUT July 12, 1960 s. l. PERssoN ETAL 2,944,804

COAL-ROCK SENSING SYSTEM Filed Sept. 9. 1958 4 sheets-sheet 4 42 VL PULSE sHAPER |ND|cAToR 40 `42A GATE F k /a 4| 43 n v n I -43a L PULSE SHAPER FIG. T

GATE GATE ToP f ToP 4 5' LEFT 52 RIGHT 4o l A 40a TNDTcAToRs 53\ ,54 BOTTOM BoTToM f LEFT RIGHT GATE GATE FIG.9

Safes :teerd wie. 196.

j 2,944,804' `COAL-ROCK sENslNG'sYsrEM Persson and William A. Leet, Rochester, l`l.Y., Rochester,

Sten I.

assignors to General Dynamics Corporation, N.Y., a corporation of Delaware Filed sept. 9, 195s, ser. Np. 759,311 s claims. (ci. 26a-'1) This invention relates to mining machines and is particularly directed to means for sensing the presence of Machines have been extensivel 'developed for continuously digging and removing the large horizontal veins of coal found in the central and eastern sections of the United States. These machines` have generally been called bore-mining machines. 'Ihe veins are quite uniform in depth, usually from threeto eight-feet, and are adapted to the bore-mining type of machine. Oneor two cutting heads are mounted on the forward end of a trackV laying tractor which carries the cutting bits in a vertical circle as the' machine moves horizontally forward along Y Fig. 2.A is an elevational view of the circle cutting area of thecutting head of the machinevof Fig. 1;

Fig. 3 is a view similar to Fig. 2 except that two cutting heads instead of one are shown;

Fig. 4 is a graph showing amplitude of -vibration of the machine of Fig. 1; Y

Fig. 5 is a cross-sectional view of one accelerometer adapted to the machine of this invention; Fig. 6 is-a graph showing the relationship of motion and time of the accelerometer of Fig. 5

Fig. 7 shows a block diagram of the circuits of invention; i v y Fig. 8 shows -a schematicY diagram ofa gate circuit; and,

Fig. 9 shows a block diagram of a comprehensive indicator system of this invention.

The bore-mining machine of Fig. 1 is of the typical track laying type comprising the tractor body 1, tracks 2, and boring head 3. The tractor follows in the tunnel dug b y the cutting head 3, the coal loosened by the head being conveyed t0 the rear of the machine and removed by the 1 conveyor mechanisms 4 and 5. The cutting head is pivand are not necessaryvfor an understanding of this inven-y the vein. `The tractor follows in the bore hole made by the cutting bits. The cutting heads are mounted'on trunnions at the forward end of the tractor to permit limited Y I 11/2 feet to 3 feet.

angular movement of the cutting'head for guiding the boring machine. The diameter of cut is selected by adjust ing radially the cutting bits seth-at the diameter ofthe bore hole isrbut slightly less than thedepth Vof the vein. AsV expected, the cutting bit will enter 'the rock boundary in the floor or the ceiling when the machine deviates butV g f little from-the center plane of the vein. Because-of the hardness of the rock usually encountered, the bits are soon;

dulled and must be replaced at considerable cost. Y Y

The object of this invention is to provide improved means for detecting the entry of a coal cutting bit into rock.

`Attempts have been made in the past to vdetect rock by measuring the heat generated at or the torque lproduced by a cutting bit. In such cases, an electrical signal generated at the bit must be transmitted through slip rings on the journal of the cutting head. v The mechanical difculties Vof mounting rock sensing devices on the cutting head `of a bore-mining machine andthe Vproblem of sparkproong slip ring circuits are obvious.

Accordingly, a Vfurther object of thistinvention is to provide means for detecting rock Without the `disadvantages of slip ring circuits.

The objects of this invention Iare attainedY by mounting two or more inertial accelerometers on the machineto sense the increased vibration thereof whenthe bit enters rock. The accelerometers are of'atype which respond to i Vmotion in one direction, only, Yand are sol oriented and.

placed onjthe frame of the machine Vas to bestfdetectxthe principal orthogonal components kof acceleration each to be described.

. A more'common oted on trunnion 6 so that the bore hole may be biased upward or downward and away from rock which may be found in either the oor or the ceiling of the vein.` Specie details of the bore-mining machine are not claimed tion. t

A typical `cutting pattern viewed in the face' of the veinl is shown in Fig. 2. The radius of the cut is adjustable on most commercially obtainable machines from about a depth of 2 inches, the angle a between the vertical and a line through the point of impact with the rock will be about 19degrees when the radius is 36 inches; the angle a will beabout 27 degrees when the radius is 18 inches'.

lf the. cutting head is turning at a speed of l7revolutions per minute, the cutting bitwill be in the rock for about .5 .Y

second. These constants will vary, of course, with-.different speeds andfdiiferent cutting radii andV yare'of portance inthe design of the electrical circuits hereinafter` vtype of bore-mining machine comprises side-,by-side cutting heads, as shown in Fig. 3, with overlapping cutting circles. There are two cutting bits on each headV Whichf'are diametrically opposedand. are

synchronizedby driving gears so that the cuttingbits alternately pass the low, or high, points in the swing'.V The cutting bits on head 1S are marked `16and 17, while the Vcutting bits on head 1 8 are marked 19 and Z0. If

Yheads 15 and 18 revolve clockwise and counterclockwise,

respectively, the bits Ywould enter the rockin the floor inthe following order: 19, 17, 20, and 16.

When the vibrations of the machine are measured at any point along the machine, from the cutting heads to the rear end, considerable rumble-type vibrations are found, as expected. lVibrations caused by the cutting of coal, impacts offalling pieces of coal, and vibrations'due time the bit passes fromfcoalinto rock. The electrical j to movements of cutter chains, conveyor linkage and gears Vcause a relatively highrbackgrou'nd of noise. AThis continuous high level vibration is indicated at l21fin Fig. 4. Each time a cutter bit enters, rock, howevelga relatively distinct movement .throughout the frame of the machine p is qualitativelyr' reported by outstanding peaks suchfas enabling the operator Yto appropriately steerk the'machine A away from the rock. l Other` objects'. andfeatures of this .invention Ywill becomeapparent'to those skilledzi 4the art by referring to the embodiments described inthe following specification and shownfin the accompanying drawings, in which:Y

chine embodying this invention;

. 'Fig'.l is a side elevational view` of a bore-mining mashown at `22Fi'g. 4. Commercial accelerometers ofivarious types rare capable of reliably identifying vibration including the sharp vibration causedby .the bit in rock.V AOne suchV accelerometer is sectioned in Fig'. 5.# The mass25` comprising a permanent magnet' in the form of a rbar of steel, iron,` or alnico is mountedto slide withrninimum friction along the axis of coil 26.

The magnet is lightly pressed with spring 27 against stopV 28 rto hold lthemagnet centrally in the coil. The coilY If the cutting tool will enter rock toV structureincluding the stop is xedly joined to the unitary mounting structure 29 which .in turn is bolted, or otherwise fastened, to the frame of the machine, the vibration or motion of which is to be measured. YThe place of attachment ofthe accelerometer'toj Athe mining machine is preferably` ajpoint of maximum travel. preferablywell removed from the center of gravity of-the machine and may be immediately ladjacent the cutting tools in the head "3 or at a point near the vrearend ofthe machine. Further, the accelerometers are so `oriented with respect to direction of maximum vibration as toyield the maximum signal output. Y

'When the machine frame and the supporting bracket 29 travels to the left, for example, the inertial mass 25 as viewed in'Fig. 5 moves to the right relatively,-whereupon the magnetic lines of force of the inertial mass cut'the coil windings anda voltage is induced. The voltage at terminals 26a is, essentially, a differential function of acceleration. When the movement resulting fromshock is of the type shown by the curve 3i?, in Fig. 6, acceleration increases from zero at time To to a maximum-at time T1, whereupon direction of motion reverses, velocity changes sign, and acceleration returns to zero at T2. Since the voltage induced in winding 26 is a function of acceleration, the voltage at 26a is a maximum during maximum accelerations, producing positiveand negativegoing loops of voltage during the two maxima of acceleration, respectively, as shown at 31 and 32, respectively. By'simple rectification, either voltage loop can be easily eliminated.

If the direction of force applied to the mining machine caused by the cutting bit at the instant of entry of the bit into rock is F1, Fig. 2, the vertical component of that force would be F2 and the horizontal component would be F3. According to this invention, the components F2 and F3 can be combined to indicate in which of the four quadrants the force F1 is applied. Two accelerometers for indicating force F3 in either direction and two additional accelerometers for indicating force F2 in either direction, respectively, will produce fourl signals which,

Vwhen properly combined, according to this invention, will reliably indicate the quadrant in which rock is encountered, and where there-are two cutting heads, as in Fig. 3, rock at the bottom left or right side and rock at the top right or left side is instantaneously indicated to the operator who can thereupon take` appropriateaction in steering the machine to move the cutting bits away from the objectionable rock.

In Fig. 7, accelerometers a@ and 41 are Vfixed to the machine, the vibration of which is to be indicated. It is'assumed, in the example of Fig. 7, that forces F2 and F3 areV to be detected. When the accelerometers are Vof the type'shown in Fig. 5, voltage output signals are generated in response to accelerations in one direction only. These directions are preferably at right `angles and preferably are oriented with the true' vertical Vand horizontal. The output signals of the accelerometers which are of the type shown in Fig. 4 are fed to pulse' Shapers l42 and 43, respectively. TheY pulse Shapers are typical ampliers with clippingcircuits for isolating the rock impact signals 22,'Fig. 4, from the backgroundV noiseof the accelerometers. The more orless rectangular pulses at the output circuits of the pulse VShapers are applied to two control circuits ofV gate 441i which will produce an output at 45 Vonly when the two inputs are of the same -sign and are coincident in time. Such a gate is sometimes termed an And gate. Av series of violent vibrations result in a Vseries of pulses at the gate during the time the cutting bit is moving in rock. These pulses may be integrated as by a simple lamp-i6.

One gate circuit which functions eliiciently is shown in detail in 'Fig 8. The two input or control circuits 42a and 43a are capacitively coupled to the bases, respectively, of two transistors having a common emitter resistor 44a.

The output circuit is connected to the upper end of 44a. In operation, current continues to flow in the collectoremitter circuits of the two transistors and through 44a, holding the output at some high potential. This potential drops only when both transistors are biased to cutoff simultaneously, thereupon the output voltage drops to some low value and remains during the coincident in time of the two negative-going input pulses. p

In Fig. 9, two additional accelerometers 41a and 40a areY added to the systemto senseforces F2 and F3 of either sign. Gate t4 is connected between accelerometers 40 and 41, gate 48 is connected between accelerometers 40 and 41a, gate 45 is connected between accelerometers 41a and 49a, and gate 50 is connected between accelerometers itin and 41. Each gate produces an output signal only when forces F2 and F3 indicate a rock impulse in one of the four quadrants. Indicators 51 and 52 indicate rock at thetop left and top right quadrants, respectively, of the cut face. Indicators 53 and 54 indicate rock at the bottom left and bottom right quadrants, respectively, of the cut face. v Y

One accelerometer only has been shown. There are numerous accelerometers of the-inertial type, and otherwise, which could be substituted. It is preferred, of course, that the accelerometers be sensitive to accelerations in one direction only. Many modifications may be made be made by those skilled in the electrical arts without departing from the scope of this invention as defined in the appended claims.

What is claimed is:

1. In Vcombination with a coal bore-mining machine having a rotary cutting head and a tractor for driving the head and carrying forwardly the head into a coal vein; means for indicating the entry of `a cutting bit into roof or floorrock comprising a plurality of inertial accelerometers atixed to said tractor, said accelerometers being of the type which produces Va voltage analogous to acceleration andbeing orthogonally arranged for responding to dierent components of vibratory accelerations imparted to said tractor by the bits of said cutting head, means for combining Ythe voltage responses Vof said accelerometers, and means for instantaneously indicating coincidence-in time of said voltages to show the direction of the resultant acceleration of the tractor and cutting head.

2. The combination comprising two accelerometers, each accelerometer being primarily responsive to accelerations in one direction, said two accelerometers being affixed to a base the vibratory aecelerations of which are to Vbe analyzed and the two accelerometers being Aoriented so that the directions of response are at right angles; an And gate circuit with two control circuits and one output circuit, saidaccelerorneters being directly coupled, respec- Y tively, to said two control circuits, and an indicating circuit coupled to said output circuit. y

3. In combination in a system for determining the direction of principal vibratory accelerationV of Va machine comprising two accelerometers, said accelerometers being alxed to said machine and so oriented as to generate signals, respectively, in response to orthogonal components of acceleration of said machine, said accelerometers being capable vof, generating a voltage analogous to acceleration, a pulse Shaper connected to the signal circuitY of each accelerometer, `an And -gate with two control circuits, said pulse Shapers being connected, respectively, to said two control circuits, and V,a y'utilization circuit connected to the output of said And gate. i

References` Cited intheile this patent VUNITED srArns PATENTS c 2,365,213 negers ;,Dec.` 19, 1944 2,613,0711 VHansel oct. 7, 1952 2,620,386 Alspaugh et al. Dec, 2, 1952 

